This application relates to the art of manufacturing electric arc welding wire and more particularly to a cleaning device for cleaning the wire after it has been drawn to the desired size.
In making solid welding wire, the outer surface of the wire also becomes contaminated with certain impurities, such as drawing compound. It has been suggested that solid wire can be cleaned by cathode cleaning using a magnetic field to rotate the arc as the electrode is progressing through a chamber or tunnel. This technique is quite complicated and expensive. It results in surface areas that are not clean. The arc is created by a voltage of 2-20 volts in a chamber filled with an inert atmosphere. A cathodic cleaning device for solid electrode wire is disclosed is Gordon U.S. Pat. No. 5,981,904. This patent is incorporated by reference herein as background information.
The present invention relates to cleaning the surface of a drawn cored electrode or welding wire, and it will be described with reference to a cored electrode; however, the invention has much broader applications and can be used for a solid welding wire, such as illustrated in Gordon U.S. Pat. No. 5,981,904. Both cored electrodes and solid welding wire are drawn to size. The drawing process is performed with a drawing compound or lubricant that accumulates on the outer surface and must be removed to prevent certain inconsistencies in the electric arc welding process performed using the welding wire. Attempts to accomplish this cleaning operation, other than those attempts illustrated in the material incorporated by reference, involve passing the wire through a plasma column. Such technique is inconsistent and is not easily incorporated into a wire manufacturing facility. Where the welding wire has been cleaned subsequent to drawing, there has been inconsistent results. Some areas of the surface of the wire were not cleaned. In addition, cleaning was expensive, slow, and required complex equipment.
The present invention overcomes disadvantages experiences in prior efforts to clean impurities from the surface of a rapidly moving welding wire, cored or solid, preparatory to it being wrapped on a spool or coiled into a transport drum. These advantages are accomplished by the cleaning device and method of cleaning welding wire constituting the present invention.
In accordance with the present invention, there is provided a wire cleaner for removing impurities from the surface of elongated welding wire, preferably a cored wire, as the wire travels along a given path. This welding wire cleaning device comprises a tunnel with a tube having a central passage surrounding the path and defining a gap between the tube and the wire moving through the tube. A power supply such as a Resonant Arc Starter by The Lincoln Electric Company is provided with first and second output terminals across which is generated an AC output current. In accordance with the invention, the current has a frequency in the range of 100-300 kHz with a magnitude of at least about 1.0 amperes. By using this power supply, the heating effect is concentrated on the outer skin of the wire. The heating of the sheath penetrates to a reference depth that is quite shallow. In the novel cleaner, a first connecter attaches the first output terminal of a power supply to the tube and the second terminal of the power supply to the moving wire by a sliding contact. Thus, the high frequency current passes through the wire along the surface of the sheath between the contact and the location of the arc in the plasma gap between the tunnel and the welding wire. This plasma arc moves along the surface and, from time to time, the polarity changes. Consequently, heating is primarily by current passing through the outer skin of the sheath. A high temperature plasma is created in the wire surrounding the gap by the arc across the gap. This plasma gap is in the general range of 0.025-0.030. Since the gap is quite small, heating is by resistance heating as current passes along the wire to the point of arcing and by conduction from the hot gases created by the arc in the small gap. In this manner, a current proportional to the output current of the power supply flows along the surface of the sheath and across the gap to heat the wire as the wire moves through the tube. This heating procedure has proved successful in removing surface impurities caused by the drawing operation or caused by leakage of core material to the exterior of a wire.
In accordance with another aspect of the invention, the novel cleaning device has an inlet for inert gas, such as argon. This gas fills the gap between the wire and the tube to prevent oxidation of the surface during the cleaning operation. To introduce the high frequency into the surface of the moving wire, each end of the tube is provided with a ring providing a sliding contact with the advancing welding wire.
In accordance with another aspect of the invention, two or more tandem located cleaning devices are used to clean the wire as it is moving along a path. In this manner, progressive surface cleaning of the wire is accomplished to assure a nascent, cleaned outer surface, which condition assures good electrical contact with the welding wire.
By using a frequency in the range of about 100-300 kHz, only the surface or skin of the advancing wire is penetrated by the currents flowing along the welding wire. This localizes the heating at the very thin outer layer of the wire to cause no metallurgical changes in the sheath being cleaned.
In accordance with another aspect of the invention, the welding wire enters the cleaning device with the sheath at an elevated temperature. The elevated temperature can be caused by the friction in the drawing die located upstream of the cleaning device.
In accordance with still another aspect of the invention, after the drawing process, the wire passes through an annealing station, where it is annealed either by resistance heating or induction heating. This causes a soft, but hot, sheath entering the cleaning device. The elevated temperature of the sheath gives a warm metal portion under the heated skin during the cleaning operation. Consequently, by using high frequency so that the reference depth is very shallow, the outer surface of the wire can be rapidly heated to a high temperature. When the wire enters the cleaning station at a low temperature, i.e. room temperature, high frequency shallow surface cleaning action is not as effective. As the high frequency current passes along the surface of the wire, the surface temperature increases rapidly. However, due to the heatsink effect of a cold sheath, the heated outer surface rapidly cools. Cleaning of impurities from the surface requires both high temperature and a protracted time at such high temperature to accomplish the desired amount of evaporation. When a cold sheath enters the cleaning device, the cold sheath quenches the heated surface and distracts from the evaporative effect of the cleaning operation. Consequently, as an aspect of the invention, the sheath or outer portion of the wire entering the cleaning device is at an elevated temperature. The elevated temperature can be accomplished by an annealing process or by the normal friction heating created by the drawing die. To use the heating of the drawing die, the cleaning device must be closely adjacent the drawing die.
In accordance with the preferred embodiment of the invention, the high frequency heating effect is by combined resistance heating and plasma heating caused by arcs between the tube and the advancing wire in the tube. In an alternative embodiment, an induction heating coil is positioned around the moving wire. Thus, the tunnel of the cleaning device is the central passage of the induction heating coil. This coil is energized with an alternating current having a frequency in the general range of 100-300 kHz and with a current at least about 1.0 amperes. An induction heating coil is also used for annealing before the cleaning step. By using high frequency, skin effect provides a very shallow reference depth. In this embodiment, the total heating of the surface is by induction heating. In the preferred embodiment, the heating is partially resistance heating and partially plasma heating.
The method of removing impurities from the surface of an elongated welding wire using the cleaning device defined above is another aspect of the invention. As the wire travels along a given path, it is initially heated at a first location on the path to a first depth. This initial heating can be by induction heating or by resistance heating. In both instances, the outer sheath or outer portion of the wire is at an elevated temperature. Thereafter, there is subsequent a cleaning operation wherein the surface of the wire is heated at a second location. This subsequent heating is to a second depth in the sheath, which second depth is less than the first depth. Consequently, the wire is heated to a fairly deep level before entering the cleaning operation. This gives a heat barrier or reservoir for the cleaning operation. Then, high frequency cleaning creates a hot outer surface. The hot surface is not immediately quenched by a cold core. The preferred embodiment involves heating and cleaning a cored electrode. However, a drawn solid electrode wire is equally capable of being processed by using the present invention.
A chamber around the induction heating coils can be evacuated by a pump to reduce the partial pressure around the heated surface. This increases the evaporation efficiency.
The primary object of the present invention is the provision of a device or method for cleaning a rapidly moving welding wire to remove impurities on the wire, which device and method is effective and does not require cathode heating or magnetic control of the heating operation as in the prior art.
Another object of the present invention is the provision of a device and method, as defined above, which device and method can be used at a standard welding wire manufacturing facility to clean impurities from the wire before it is packaged in a spool or coiled in a drum.
These and other objects and advantages will become apparent from the following description taken together with the accompanying drawings.